The use of an electric motor to rotate a fan blade to create an airflow has long been known in the art. Unfortunately, such fans produce substantial noise, and can present a hazard to children who may be tempted to poke a finger or a pencil into the moving fan blade. Although such fans can produce substantial airflow (e.g., 1,000 ft3/minute or more), substantial electrical power is required to operate the motor, and essentially no conditioning of the flowing air occurs.
It is known to provide such fans with a HEPA-compliant filter element to remove particulate matter larger than perhaps 0.3 μm. Unfortunately, the resistance to airflow presented by the filter element may require doubling the electric motor size to maintain a desired level of airflow. Further, HEPA-compliant filter elements are expensive, and can represent a substantial portion of the sale price of a HEPA-compliant filter-fan unit. While such filter-fan units can condition the air by removing large particles, particulate matter small enough to pass through the filter element is not removed, including bacteria, for example.
It is also known in the art to produce an airflow using electro-kinetic techniques, by which electrical power is converted into a flow of air without mechanically moving components. One such system is described in U.S. Pat. No. 4,789,801 to Lee (1988), depicted herein in simplified form as FIGS. 1A and 1B and which patent is incorporated herein by reference. System 10 includes an array of first (“emitter”) electrodes or conductive surfaces 20 that are spaced-apart symmetrically from an array of second (“collector”) electrodes or conductive surfaces 30. The positive terminal of a generator such as, for example, pulse generator 40 that outputs a train of high voltage pulses (e.g., 0 to perhaps +5 KV) is coupled to the first array, and the negative pulse generator terminal is coupled to the second array in this example. It is to be understood that the arrays depicted include multiple electrodes, but that an array can include or be replaced by a single electrode.
The high voltage pulses ionize the air between the arrays, and create an airflow 50 from the first array toward the second array, without requiring any moving parts. Particulate matter 60 in the air is entrained within the airflow 50 and also moves towards the second electrodes 30. Much of the particulate matter is electrostatically attracted to the surfaces of the second electrodes, where it remains, thus conditioning the flow of air exiting system 10. Further, the high voltage field present between the electrode arrays can release ozone into the ambient environment, which can eliminate odors that are entrained in the airflow.
In the particular embodiment of FIG. 1A, first electrodes 20 are circular in cross-section, having a diameter of about 0.003″ (0.08 mm), whereas the second electrodes 30 are substantially larger in area and define a “teardrop” shape in cross-section. The ratio of cross-sectional radii of curvature between the bulbous front nose of the second electrode and the first electrodes exceeds 10:1. As shown in FIG. 1A, the bulbous front surfaces of the second electrodes face the first electrodes, and the somewhat “sharp” trailing edges face the exit direction of the airflow. The “sharp” trailing edges on the second electrodes promote good electrostatic attachment of particulate matter entrained in the airflow.
In another particular embodiment shown herein as FIG. 1B, second electrodes 30 are symmetrical and elongated in cross-section. The elongated trailing edges on the second electrodes provide increased area upon which particulate matter entrained in the airflow can attach.
While the electrostatic techniques disclosed by the '801 patent are advantageous over conventional electric fan-filter units, further increased air transport-conditioning efficiency would be advantageous.
Ion wind devices such as those described in U.S. Pat. No. 4,789,801 provide accelerated gas ions generated by the use of differential high voltage electric fields between an array of one or more emitters and a plurality of collectors (accelerators). The ions are entrained in the ambient bulk gases, causing the gases to flow. Gas velocities can reach as high as eight hundred feet per minute. However, the high voltage electric fields used to generate the gas ions and provide the force necessary for gas acceleration are also responsible for creating molecular disassociation reactions, the most common of which include ozone generated from oxygen when such devices are operating in a breathable atmosphere. The U.S. Food and Drug Administration has determined that indoor, airborne ozone in concentrations above 50 ppb (parts per billion) may be hazardous to humans. NIOSH (National Institute of Occupational Safety and Health) has ruled that indoor concentrations of ozone above 100 ppb may be hazardous to humans. Devices which utilize high voltage electric fields to generate atmospheric plasma, corona discharge and air ions, are all susceptible to generating this allotropic of oxygen, ozone. There exists a linear relationship between the level of the high voltage fields and current and the level of ozone concentration in most direct current operated ion wind systems. Also, a linear relationship exists between the acceleration velocity and intensity of the electric fields. Typically, the higher the voltage the higher the acceleration. Since it is desired to have maximum acceleration, methods must be employed to reduce ozone production or convert unwanted ozone back to oxygen before it is expelled into the breathable atmosphere. It is an object of this invention to provide methods to convert generated ozone back to oxygen in such devices.
Ion wind devices that have been specifically designed as air cleaners have also been inherently limited in their airflow and in the amount of particle contamination they can remove. Unlike electrostatic air cleaners that rely upon a motor driven fan to propel air into an ionizing field, the ion wind device utilizes a structured ionizing field as the primary air movement force. This requires molecular ionization levels at many orders of magnitude greater than are used in electrostatic precipitator devices. Consequently, like-charged particles and matter clustered in the air stream inhibit some airflow and precipitation ability of ion wind devices. It is a further object of this invention to teach a method and apparatus for de-ionizing a large portion of the charged molecules responsible for the resisting forces in the air stream and to improve precipitation efficiency of the charged contaminant particles by accelerating them towards an oppositely charged collector plate array.